The only time I was ever knocked unconscious was off a bike. I was cycling with my friend, age 13 or so, and hit [[something]] at the bottom of a hill, to this day I don't know what it was. It buckled my shitty bike's front wheel and sent me over the handlebars, into the ground, and into unconsciousness for about a minute, according to my friend, who was traumatised.
Took an ambulance ride to hospital because I might have had a concussion, but they didn't put the sirens on so it took an hour and a half and by the time I got there, anyone in the ambulance could tell I was fine. NHS everyone!